The invention relates to a displacement unit with a tubular outer part, the inner face of which has outer running tracks at least in part, with an inner part which is axially displaceable in the outer part and the outer face of which has inner running tracks at least in part, and with balls arranged for torque transmission, respectively, in outer running tracks and inner running tracks associated with each other in pairs. The invention further relates to a jointed shaft with a displacement unit.
Displacement units of this type are known, for example, from U.S. Pat. No. 6,234,908 (=DE 198 31 010), U.S. Pat. No. 6,241,617 (=DE 198 31 016) and U.S. Pat. No. 6,306,045 (=DE 199 11 111) and are used to offset or compensate for a telescopic displacement, which is necessary for assembly and/or occurs in operation of a shaft that is used, for example, in the drivetrain of a motor vehicle. Beyond the normal displacement path that is provided in these displacement units in operation or is possible during assembly, a further axial telescoping of the displacement unit or the shaft connected therewith is not provided or possible.
In a head-on collision of a motor vehicle, the entire vehicle is partially strongly compressed, depending on the severity of the collision. As a result, a substantial partial axial load acts also on the longitudinal vehicle driveshaft. To safely prevent the shaft from buckling and penetrating the passenger compartment, the shaft must therefore be capable of axially contracting. In the known displacement units, this is possible only to a very limited degree, so that the longitudinal shaft can buckle and can potentially endanger the vehicle occupants.
Further, in U.S. Pat. No. 6,379,255 (=DE 199 43 880) a drive arrangement is proposed in which two shaft sections of a longitudinal drive shaft are interconnected by a center joint. The diameters of the two shaft sections are such that the shaft sections can telescope into each other in case of a collision. To this end the cage of the center joint is constructed as a predetermined breaking point which fails in a collision and thereby enables the two shaft sections to telescope. In addition, the transmission-side joint and the differential-side joint are constructed as slip joints. Particularly in applications requiring relatively large, non-destructive changes in the axial length of the drive shaft for assembly and/or in operation, the comparatively small non-destructive displacement path of the slip joints has proven to be a disadvantage in this known drive arrangement.